The use of composite materials or laminates such as wall coverings as decorations for interior walls is long extant. In fact, wall coverings can be seen in revolutionary war era homes. Traditionally, the use of such wall coverings was associated with quite cumbersome installation. Once the wall covering was actually in place, it often became stained and showed other aspects of wear. Many developments in the wall covering art, particularly relating to plastic wall coverings, have attempted to address these problems. However, none of these attempts has been applicable to non-textured, wall covering substrate without considerable, undesirable characteristics being associated therewith.
Modern wall coverings are quite complex in their composition when compared to the wall coverings used in the past. For instance, modern wall coverings are frequently paperbacked colored PVC film or duplex paper (double paper layer) to prevent bleed-through of an adhesive used to bind the wall covering to a wall or other interior surface. The duplex wall covering also adds dimensional strength to the material, i.e. adds a certain degree of stiffness, providing for greater ease of installation. Paperbacking also insures proper drying of the installation adhesive especially on materials that are non-porous, i.e. materials commonly used in wall coverings such as polyvinylchloride (PVC) film. Still another reason for the increased use of duplex materials is that the paperbacking has great benefit in hiding any imperfections on the wall that would tend to pattern or cause an irregular surface on the face of the wall covering subsequent to installation. Also, should removal of the wall covering be desired, duplex materials facilitate wall covering removal because a thin layer of paper remains on the wall preventing any damage that may occur to a plaster wall or other wallboard upon wall covering removal. Therefore, materials comprised as a duplex structure are particularly suitable for use as a wall covering.
Certain problems are particularly unique to printed wall coverings. Although such wall covering grounds (that is, the material to be printed on or a wall covering without printing) may be washable, such as paperbacked PVC, once the wall covering is imprinted with a pattern, it is substantially less resistant to stains. This decrease in stain resistance is more or less proportional to the amount of print coverage on the wall covering. Therefore, the more ink or print coverage on the wall covering, the less washable and stain resistant is the wall covering.
A large number of laminate films and film adhesives are known in the wall covering art. Various combination of such films and adhesives have been used in the manufacture of wall coverings. However, as reviewed above, problems with certain of these adhesives and films in combination have been apparent. One of the significant difficulties in combining laminate films and adhesives is the unpredictability of commercially important traits of the film and adhesive after being combined. There is no known way to predict if the combination of a film having desired characteristics and an adhesive having desired characteristics will yield a film/adhesive combination with desirable characteristics. An example of this unpredictability can be seen in the use of polyvinylchloride having polymeric plasticizer and polyvinylchloride having monomeric plasticizer. When examined alone, i.e. not in combination with an adhesive, both types of PVC would appear to have similar characteristics and provide similar utility. However, these PVC's behave differently when combined with different types of adhesive.
When determining which adhesive manifests the appropriate characteristics desirable for combining with laminate films, it is common to examine clarity of the dried adhesive on light and dark colored surfaces, resistance to light (UV light in particular), ability to stick to non-porous surfaces, as well as other qualitative characteristics such as peel and sheer. Different characteristics are significant when selecting an appropriate film laminate for the combination. Among the parameters which must be evaluated in film and adhesive selection are clarity, lay flat, adhesion, foldability, and color fastness.
It will be appreciated that many of these criteria are qualitative. For instance, a certain degree of yellowing may be acceptable if it is essentially imperceptible when the wallpaper is on the wall. Similarly, the precise degree of lay flat or memory acceptable is a qualitative determination made by the manufacturer. However, there certainly reaches a point at which all manufacturers would agree that a wall covering exhibits characteristics that are quite unacceptable as to each of the afore-designated parameters. As used herein, the following definitions are provided for these qualitative characteristics.
"Clarity" is essential when laminating a clear surface laminate film onto a wall covering substrate. Lack of clarity results in streaking, discoloration, and cloudiness which blur or otherwise distort the normal appearance of the wall covering. In addition, certain peculiar, undesirable side effects associated with clarity come into play regarding the use of certain colors in combination with certain adhesives. For instance, the use of an aqueous based adhesive when laminating a surface laminate film to navy blue paper causes accentuated discoloration probably because of solids in the adhesive. Also, different adhesives provide different degrees of clarity depending on the degree of darkness or lightness on the surface.
"Lay flat" is a descriptive term which characterizes the degree of resilient curl which a material possesses when it is unrolled or laid out on a flat surface. This characteristic is commonly found, for instance, in gift wrapping paper which when removed from a roll has a tendency to reform into a cylinder if not held in the flat position. A wall covering which has good lay flat will not curl. When unrolled and laid on a flat surface, wall covering exhibiting good lay flat has very limited tendency to curl. Good lay flat is very important in facilitating application of wall covering to an interior surface.
"Adhesion" defines the strength of bonding between two materials. The harder it is to separate or peel away two substrates, i.e. an adhesive and a surface laminate film, the greater is the adhesion. Adhesion has nothing to do with adhesive tackiness. An adhesive can be quite tacky and have poor adhesion.
Wall coverings must be foldable. "Foldability" characterizes the trait of a wall covering to fold whether inwardly (printed surface to printed surface) or outwardly (back to back.) When wall covering is folded, it should fold with equal facility either inwardly or outwardly. However, when making such folds, the wall covering should not wrinkle or show damage along the fold but rather fold sharply and crisply so, for instance, it can be wrapped around corners of a wall without adversely affecting the appearance of the wall covering.
"Color fastness" refers to the ability of surface laminate films and adhesives to not interfere with the high quality color characteristics of the wall covering. Oftentimes, colors will run, blur, show different colorations, or otherwise have their appearance altered in the course of the processing necessary to bind a clear surface laminate film/adhesive combination to the wall covering substrate.
"Migration" refers to movement of plasticizer out of the laminant film. It is common for the plasticizer used in the surface laminate film to migrate through the layers of the lamination causing an undesirable appearance. Most commonly, this occurs when plasticizer migrates into the adhesive. One manifestation of such a migration is the delamination of surface laminant film, while plasticizer migration into an adhesive may result in surface laminate film shrinkage and adhesive spoilage.
Selection of the proper plasticizers, e.g. whether polymeric or monomeric, is important. Generally plasticizers have a tendency to migrate out of film causing film shrinkage. This is especially disadvantageous if shrinkage occurs after application of the wall covering to an interior surface. The result is seam separation and other irregularities on the wall covering. Plasticizers can migrate into the adhesive causing the adhesive to become softer and stickier, both undesirable traits. Moreover, plasticizer migration into the adhesive accelerates the aforementioned shrinking problem because the softer adhesive creates a less viscous medium in which the film can move and therefore the speed of shrinking is not inhibited. In aging tests conducted in conjunction with this invention, it was shown that polymeric plasticizers combined with surface laminate films showed no negative migration results after three months at conditions of 105.degree. Fahrenheit and 85% humidity. Such was not the case when monomeric plasticizers were used. Use of monomeric plasticizers revealed unacceptable migration characteristics.
Acrylic adhesives were found to be the adhesive of choice especially in surmounting clarity problems. When water disbursed adhesives were used, they were generally unsatisfactory especially with regard to clarity on dark colored wall covering surfaces.
As previously noted, the characteristics which will result from a combination of a particular laminate film and a particular adhesive are unpredictable even when the characteristics of such film and adhesive alone are known. For instance, polyvinylchloride with monomeric plasticizer and polyvinylchloride with polymeric plasticizer would appear to be acceptable laminate films in all significant characteristics. Both have desirable lay flat, memory, pliability, foldability, clarity, scratch resistance, surface porosity, surface bondability, stretchability, and reaction to heat. It would thus appear that polyvinylchloride film with both monomeric and polymeric plasticizer is an ideal film. However, when these films are combined with adhesives manifesting the appropriate, desirable characteristics of, for instance, clarity on colored surfaces, peel, ability to bind to non-porous surfaces, sheer, and UV resistance each film performs differently.
It is, therefore, an object of this invention to create a composite material or laminate, e.g. wall covering, or the like, having desirable wear and stain resistant characteristics.
It is another object of this invention to provide a means for achieving desired durability and wipability of wall covering substrates while simultaneously providing an economically and commercially feasible process.
The combination of film and adhesive which manifested the commercially desirable characteristics was the combination using PVC polymeric plasticized film and acrylic adhesive. This particular combination, not others, overcomes the aforediscussed difficulties. By this combination, the instant invention provides for much greater stain resistance, washability and wearability of wall covering substrates. This has been accomplished while preserving all the beneficial aspects of duplex wall covering. Moreover, the particular process used provides results which cannot be had with numerous other combinations of clear films and adhesives.